Current Share in Multiphase DC–DC Converters Using Digital Filtering Techniques

This paper introduces a new method of passive current balancing for digital control of multiphase DC-DC converters based upon the duty-cycle-matching principle. Current balance is achieved by inserting a digital filter into the control path. The method does not rely on a current balancing loop, and therefore, the stability and performance concerns associated with the traditional current balance loop are obviated. Being sensorless, it is insensitive to current measurement inaccuracies caused by noise, component value tolerance, or variation. It will be shown that effective current balancing can be achieved via some simple modifications to standard voltage-mode control laws, allowing current balancing to be achieved with minor additional complexity. The effectiveness of the method has been demonstrated by experimental validation of a multiphase DC-DC converter. The current share scheme has been shown to perform well dynamically, matching currents cycle by cycle during load steps, and clearly benefiting from the absence of the slow current share loop popular in traditional methods. The proposed current share filter blends well with existing digital controllers. Given the very low complexity in implementing the filter, the degree of matching achieved is exceptional.